Compositions of matter comprising at least two elements, molecules, grains, crystals, structural units, or phases of matter, and more particularly to metal alloys, mixtures of metals and metal oxides, mixed composition semiconductors, and mixed organic and inorganic substances, wherein the scale of mixing of the reactants may be on the order of nanometers or less; and wherein the resulting distribution of elements, molecules grains, crystals, structural units, or phases of matter may range from nanometers to about one millimeter; and processes for preparing these compositions of matter as thin films or particles.
There is a large demand for multi-component substances across a range of technological and industrial applications. These multi-component substances may be required for particular applications as thin films for use in optical and opto-electronic devices, as insulating and diffusion barriers in silicon-on-insulator electronic devices, chemical sensors, MEMs, pyroelectrics and superconducting films among others. Alternatively, such multi-component substances may be required for other applications as fine particles, or powders, for use in structural materials, pharmaceuticals, medical devices, separation processes, catalysis, and others.
The present invention provides a method and apparatus for the synthesis of multi-component substances, comprising entities of at least two elements, molecules, grains, crystals, structural units, or phases of matter, in which the scale of the distribution of the elements, molecules, or phases of matter may range from on the order of nanometers or less, to about one millimeter, depending upon the specific materials and process conditions that are chosen. The method and apparatus of the present invention further provides processes for preparing these compositions of matter as thin films or particles. The present invention additionally provides examples of such substances.
In regard to the term xe2x80x9cmulti-componentxe2x80x9d, as used herein, a xe2x80x9ccomponentxe2x80x9d is defined as an entity, which is either a discontinuous material distributed throughout another material; or a generally continuous material, through which is distributed other materials. Thus, in the present invention, a component may be a pure element, distributed throughout or coated upon a general continuous phase of matter, such as titanium metal, cerium metal, silicon, or other elements. A component may be a molecular substance, or an inorganic or ionic compound distributed throughout or coated upon a general continuous phase of matter, such as gallium nitride, silicon carbide, zinc oxide, titanium nitride, cerium oxide, hafnium oxide, and the like. A component may be a grain or crystal structure within a metal alloy wherein different grains or crystals within the alloy comprise different compositions, e.g. a particular metal that has a specifically advantageous grain structure. A component may be a first structural unit of matter, distributed throughout a second phase of matter, e.g. fibers, nanotubes, or nanospheres distributed throughout e.g. a polymer, a glass, and the like, such as a catalytic metal distributed within a matrix structure; or cerium oxide (CeO2, or Ce2O3) or silicon oxide (SiOx, where x is 1 or 2). A component may be an inorganic phase of material distributed throughout or coated upon an organic phase of matter, or vise versa, such as an organic dye condensed within a continuous inorganic thin film; or a dye embedded in an inorganic matrix; or sequentially layered combinations of such films. A component may be a substantially continuous phase of matter through which other components are distributed or coated upon as defined above.
The single feature in common with all of the above variants of components is that they each are products resulting from the process of the present invention. Accordingly, novel materials produced by the process of the present invention may comprise two or more components selected from elements, molecules, inorganic or ionic compounds, grains, crystals, structural units, and phases. The components, while most often being present as solids, may also exist as liquids or gases in the materials of the present invention.
The unique capabilities of the energy assisted molecular beam deposition processes of the present invention, including pulsed arc molecular beam deposition (PAMBD), laser assisted molecular beam deposition (LAMBD), and electron beam assisted molecular beam deposition (EAMBD), enable the instantaneous mixing of reactive chemical species on a molecular scale, such that the resulting film or powder products have uniform repeating structures distributed through them which may range from nanometers or less, to about one millimeter. For example, metal alloys with extremely fine grain structure can be produced by the PAMBD process. Such unique metal alloys are valuable as e.g. heterogeneous catalysts, sensor elements, and high strength materials.
Mixed organic and inorganic matrices may also be synthesized in thin film or particulate form. For example, one may synthesize metal/metal oxide films doped with organic or covalent molecules; or metal/metal oxide particles coated with organic films. One may further synthesize an organic dye or pigment encased within a metal oxide matrix. Such materials prepared as thin films are known to possess non-linear optical properties, which are useful in photonic applications. Other such materials, comprising an organic photoconductive material dispersed in a second electron and/or hole transporting material, are useful in the practice of electrophotography.
The process of the present invention may also be used to synthesize films of mixed composition semiconductors, which comprise tunable band gap materials. For example, one could synthesize a film comprising gallium nitride and scandium gallium nitride in various proportions. Such tunable band gap semiconductors are useful as blue, white, or short wavelength display and sensor devices, photon emitters or detectors, and transistors, used in the display, lighting, sensing, communications, and electronics industries.
Multi-layer films on the order of nanometers thick may also be synthesized by the process of the present invention. Such films of alternating layer composition are useful as e.g., low pass, high pass, or cutoff optical filters, and sensor elements.
In all of these cited examples of the present invention, the compositions of matter and the material properties obtained are difficult or impossible to obtain using material synthesis, film coating, and particulate generating processes of the prior art. For example, there is currently no satisfactory method to generate high optical quality scandium gallium nitride and other gallium nitride based materials. The pulsed arc molecular beam and laser assisted molecular beam processes of the present invention are superior in producing these materials, and many other materials.
It is therefore an object of this invention to provide a simple process for the synthesis and deposition of thin films comprising multi-component substances with an ordered structure on the scale of between one nanometer and one millimeter.
It is a further object of this invention to provide a simple process for the synthesis and harvesting of powders comprising multi-component substances with an ordered structure of between one nanometer and one millimeter.
It is another object of this invention to provide a process for the synthesis and deposition of thin films comprising multicomponent substances with an amorphous or disordered structure.
In accordance with the present invention, there is provided a process for making a multi-component substance of at least two elements, molecules, grains, crystals, structural units, or phases of matter, wherein the scale of distribution of elements, molecules, inorganic or ionic compounds, grains, crystals, structural units, or phases of matter is on the order of nanometers or less, to as much as one millimeter, comprising the steps of applying energy from an energy source to a first target assembly wherein said first target assembly is comprised of a first material and a second material, ablating said first material from said first target assembly and generating a first plasma, ablating said second material from said first target assembly and generating a second plasma, discharging a flow of reagent gas from a gas supply toward said first plasma, discharging a flow of reagent gas from a gas supply toward said second plasma, reacting said first plasma and said second plasma to produce a multi-component substance, discharging a flow of reagent gas from a gas supply toward said harvesting device, and harvesting said multi-component substance with said harvesting device.
One aspect of the invention is based on the discovery of techniques to simultaneously utilize a high temperature plasma source as a chemical reactor, and as a molecular beam. This technique enables the generation of unique combinations of reactants in a highly energetic, yet controlled environment, such that novel reaction products are produced. These novel materials may be collected as thin films on a substrate, or harvested as fine powders.
Such techniques can be generally implemented, by applying energy from an energy source upon a target material, which produces a plasma within a generation chamber or localized zone or localized region. Concurrently, a pulse of reagent gas is directed into the generation chamber, which mixes with the plasma, and which subsequently transports the mixture into a deposition/harvesting chamber. There is a vast array of candidate target materials and reagent gases which may be selected as reactants. Accordingly, a considerable range of novel materials may be produced by the process of the present invention.
A further aspect of the invention is based on the observation of problems with conventional energy-driven material processes performed in vacuo. For example, pulsed laser deposition (PLD) is a process in which a target material is simply ablated within a chamber, in proximity to a substrate. Coating of the substrate with ablated material occurs. However, the PLD process typically produces a volcanic-like eruption of vapor, fine particles, and larger debris from the target surface, resulting in a film or powder of non-uniform chemical composition and morphology. In contrast, the process of the present invention produces a controlled generation of target material into a plasma, and a controlled transport of the target material to a substrate or into a harvesting chamber. The resulting film and/or powder materials produced by the present invention are superior to those achieved by processes of the prior art in that they are more uniform in chemical composition and in morphology. In addition, the process of the present invention enables the synthesis of a multi-component substance of at least two elements, molecules, inorganic or ionic compounds, grains, crystals, structural units, or phases of matter, wherein the scale of distribution of elements, molecules, inorganic or ionic compounds, grains, crystals, structural units, or phases of matter may range from nanometers or less to about one millimeter.
The technique described above is therefore advantageous because it enables the synthesis of a broad range of high purity materials with ordered nanostructures, which provide the materials with useful properties. The materials may be synthesized as powders or as thin films, which further provide the materials with useful functions.